1. Field of the Invention
The present invention relates to roller shutters for windows or doors and particularly to a method for manufacturing and assembling slats for such shutters.
2. Description of the Prior Art
Articulated slat roller shutters in which the individual slats are either extruded of plastic resin or rolled from aluminum strip are used in residential and some commercial applications to control light and heat transmission through windows, as well as to provide privacy. The extruded plastic type of shutter requires added steel or aluminum reinforcing ribs if it is to be used for very large windows. The rolled aluminum shutter slats are strong enough for all normal application; however, special rolling dies and machinery are required to form the slats from flat aluminum strip. This equipment is extremely expensive and represents a very high initial investment. It would be desirable, therefore, to be able to extrude such aluminum slats using conventional extrusion presses and a relatively inexpensive die for forming the desired cross-sectional shape of the salt. In addition, extruded aluminum can be easily anodized or painted, whereas rolled strip aluminum cannot be.
To provide an easily assembled articulated joint shutter, the extruded plastic slats (and also the rolled aluminum slats), of the type mentioned above, normally are formed with a curled lip, hook-like in cross section, extending along one edge and an undercut slot extending along the opposite edge. The hooked lip of one slat fits slidably in the undercut slot of an adjacent slat, the opening of the undercut slot being narrow enough to prevent the curled hook portion of the lip from coming out of the slot when the slats are assembled to make a roller shutter.
Because the extrusion die is machined with openings corresponding to the solid parts of the cross section of the extruded slat, and vice-versa, the die will have a solid portion, corresponding to the shape of the interior of the undercut slot, which is joined to the rest of the die only by a thin neck, corresponding to the narrow opening of the slot. This presents no problem at the relatively low pressures used for extruding plastic resin materials. Aluminum extrusion requires much higher pressures, however; so that a die shape designed for extruding a plastic shutter slat cannot be used for extruding aluminum.
As mentioned above, the slats fit slidably together, with the hooked lip of one slat being engaged within the undercut slot of the adjacent slat. To prevent the slats from sliding longitudinally after assembly, which could cause the shutter to jam when being rolled up or down, a friction clip is inserted into each end of each slat as the shutter is assembled. It would be desirable to eliminate the extra cost and time of assembly of these clips, as well as to provide a more secure lock against relative sliding of the slats in the assembled shutter.